Monster frequency

The term monster frequency applies to random monsters generation, as opposed to deliberate polymorph results and more specific ways of monster generation. It refers to a number which can technically range 0-7 (though 6 and 7 are not used) used internally to determine how frequently a monster is generated; it can be thought of as a relative probability that a particular monster will be selected.

When a monster is randomly being selected, the game picks a random monster subject to the following list of conditions with relative probabilities equal to the ratios of numberic monster frequencies (thus a monster with a 4 is twice as common as a monster with a 2); this can be thought of as generating a list of monsters with each monster appearing a number of times equal to its monster frequency and choosing purely randomly off of this list.

Randomly generated monsters must be:

No greater in difficulty than the average of the level's difficulty and the player level [1]

No lower in difficulty than one-sixth that of the current level's difficulty[2]